This invention relates to polybutylene modified masterbatches used in the preparation of impact resistant polypropylene with enhanced properties. More particularly, a masterbatch comprising an elastomer, a butene-1 polymer and an optional co-modifier affords a polypropylene with improved properties, notably impact resistance, elongation properties and weld line strength.
High impact polypropylene (HIPP) having a flexural modulus of between 115,000 psi and 200,000 psi is conventionally produced by blending into polypropylene an impact blend consisting of a rubber such as an ethylene-propylene-diolefin elastomer (EPDM) and a co-modifier such as high density polyethylene (HDPE). The impact blend is typically "let down" into polypropylene by mixing pellets of the blend and polypropylene and extruding the mixture. While the addition of a rubber generally results in improved impact strength, the resulting HIPP may exhibit loss of weld line strength or ductility. It has now been discovered that substitution of a butene-1 polymer for all or a portion of the co-modifier used with the rubber in the impact blend, affords HIPP while avoiding these undesirable property changes in the finished product.
U.S. Pat. No. 4,078,020 discloses a thermoplastic elastomer composition which has a flexural modulus of between 4,000 and 109,000 psi comprising polypropylene, polybutylene and from 20 to 80% by weight of an elastomeric material such as an EPDM. The three components are blended to flux in a mixer; a masterbatch technique is not used. The composition has a higher rubber content and very low stiffness values, and does not exhibit the enhanced weld strength of HIPP prepared according to the present invention.
U.S. Pat. No. 3,455,871 discloses a masterbatch technique where butene-1 polymers are used as carriers to disperse additives in other polymers. The additives are described as non-olefinic materials such as pigments and lubricants, as opposed to the rubber or rubber/co-modifier mixed with the butene-1 polymer in the masterbatches herein.